I am not familiar with Open Graph, but I think that is something facebook does internally you would have to check how they render the link, by inspecting it perhaps they further open a embed iframe or something which would be it.
I will give a look at the Open Graph code used on mattermost to see if it does anything different with videos as well.
Well I tried with a random facebook video and it doesn’t convert it into a video like u said above:
Perhaps you can provide me with a facebook URL that does?
I’ve also checked the open graph code and don’t see anything special there for videos.
There is however, a file preview for files you have uploaded directly that will preview it as video/audio if the file type is such.